Silica-based glass, such as soda-lime glass, is commonly used in the manufacture of glass containers and other products. During the melting process, raw materials typically are mixed and then fed into a glass melter. The glass typically has a residence time in a furnace on the order of twenty-four hours to refine the glass by driving off gases as the raw materials decompose to oxide forms and melting the oxides to provide a homogenous glass melt. One of the rate-limiting steps in this process is called “refining,” sometimes referred to as “fining,” which is the process of removal of gas bubbles from the glass melt. If not removed, these bubbles can remain in the finished object, and can be objectionable for reasons including strength and aesthetics. In addition to being undesirably slow, this in-furnace refining process involves a large amount of space and high energy input.
A general object of the present disclosure is to provide a process for making silica based glass, which is more rapid and requires less energy input than conventional processes.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
A process for making a silica-based glass, in accordance with one aspect of the present disclosure, includes: (a) reacting at least one glass network former and at least one glass network modifier to form a glass precursor melt, the glass precursor melt having a viscosity of not more than 30 Pa·s, preferably less than 15 Pa·s and most preferably less than 8 Pa·s, when measured at a temperature of 1300 C. by an Orton RSV-1600 viscometer using an Orton part number 13-1500 spindle, and (b) refining the glass precursor melt. Other viscosity measuring techniques can be employed.
Either or both steps (a) and (b) can be carried out under reduced pressure or other method to enhance refining. Additional raw materials can then be added to the refined glass precursor melt to yield the desired glass composition. Typically this composition can have a viscosity above 30 Pa·s when measured at 1300 C. These additions preferably include glass network former materials including silica (SiO2). Cullet, frit and/or minor ingredients such as colorants can be added at this stage.